IJRET : International Journal of Research in Engineering and Technology is an international peer reviewed, online journal published by eSAT Publishing House for the enhancement of research in various disciplines of Engineering and Technology. The aim and scope of the journal is to provide an academic medium and an important reference for the advancement and dissemination of research results that support high-level learning, teaching and research in the fields of Engineering and Technology. We bring together Scientists, Academician, Field Engineers, Scholars and Students of related fields of Engineering and Technology.

1. IJRET: International Journal of Research in Engineering and Technology eISSN: 2319-1163 | pISSN: 2321-7308
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Volume: 03 Special Issue: 03 | May-2014 | NCRIET-2014, Available @ http://www.ijret.org 410
DESIGN OF DUAL MASTER I2
C BUS CONTROLLER
Ashwini s. Tadkal1
, Padmapriya Patil2
1
M Tech (Final year), VLSI, VTU Regional centre Gulbarga, Karnataka, India
2
Assistant professor, Electronics and communication, PDA College Gulbarga, Karnataka, India
Abstract
This paper presents an experimental design and implementation of serial data communication using I2C (Inter-Integrated Circuit)
multi master and multi slave bus controller using a field programmable gate array (FPGA). The I2C master bus controller was
interfaced with slave. This module was designed in Verilog HDL and simulated in Modelsim 10.1c. The design was synthesized using
Xilinx ISE Design Suite 14.2. I2C master initiates data transmission and in order slave responds to it. It can be used to interface low
speed peripherals like motherboard, embedded system, mobile phones, set top boxes, DVD, PDA’s or other electronic devices.
Keywords – FPGA, I2
C, master, Modelsim, serial data communication, slave, Spartan 3AN, Xilinx.
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1. INTRODUCTION
In the world of serial data communication [5], there are protocols
like RS-232, RS-422, RS-485, SPI (Serial peripheral interface),
Micro wire for interfacing high speed and low speed peripherals.
These protocols require more pin connection in the IC(Integrated
Circuit) for serial data communication to take place, as the
physical size of IC have decreased over the years, we require less
amount of pin connection for serial data transfer.
USB/SPI/Microwire and mostly UARTS are all just one point to
one point’ data transfer bus systems. They use multiplexing of
the data path and forwarding of messages to service multiple
devices. To overcome this problem, the I2
C [1] protocol was
introduced by Phillips which requires only two lines for
communication with two or more chips and can control a
network of device chips with just a two general purpose I/O pins
whereas, other bus protocols require more pins and signals to
connect devices.
In this project, we are implementing multi master and multi slave
I 2
C bus protocol for interfacing low speed peripheral devices on
FPGA It is also the best bus for the control applications, where
devices may have to be added or removed from the system. I2
C
protocol can also be used for communication between multiple
circuit boards in equipments with or without using a shielded
cable depending on the distance and speed of data transfer. I2
C
bus is a medium for communication where master controller [6]
is used to send and receive data to and from the slave. The low
speed peripheral, is interfaced with I2
C master bus and
synthesized on Spartan 3AN.Fig-1 shows the I2
C bus system
with multi master and multi slave.
When using multiple master Arbitration and clock stretching
need to considered. Arbitration decides which master is going to
rule the bus.
The synopsis of the paper is as follows: In section 2, we
discussed I2C protocol of our proposed design which also
presents module description for our proposed system. In section
3, we present the software implementation along with algorithm
and flow chart.. Finally, concluded with future scaleup in section
4.
Fig-1 I/O Diagram of I2
C Multi Master and Multi Slave bus
controller
2. PROPOSED WORK
2.1. I2
C Protocol
I2
C is a two wire, bidirectional serial bus that provides effective
data communication between two devices. I2
C bus supports many
devices and each device is recognized by its unique address.
The physical I2
C bus consists of just two wires, called SCL and
SDA. SCL is the clock line. It is used to synchronize all data
transfers over the I2
C bus. SDA is the data line. The SCL and
SDA lines are connected to all devices on the I 2
C bus. As both
SCL and SDA lines are "open drThe I2
C bus is said to be idle
when both SCL and SDA are at logic 1 level. When the master
(controller) wishes to transmit data to a slave (DS1307) it begins
by issuing a start sequence on the I2
C bus, which is a high to low
transition on the SDA line while the SCL line is high as shown in

2. IJRET: International Journal of Research in Engineering and Technology eISSN: 2319-1163 | pISSN: 2321-7308
__________________________________________________________________________________________
Volume: 03 Special Issue: 03 | May-2014 | NCRIET-2014, Available @ http://www.ijret.org 411
Fig– 2(a).The bus is considered to be busy after the START
condition. After the START cond
Fig- 2 (a) “START” Sequence (b) “STOP” Sequence
slave address is sent by the master. The slave device whose
address matches the address that is being sent out by the master
will respond with an acknowledgement bit on the SDA line by
pulling the SDA line low. Data is transferred in sequences of 8
bits. The bits are placed on the SDA line starting with the MSB
(Most Significant Bit). For every 8 bits transferred, the slave
device receiving the data sends back an acknowledge bit, so
there are actually 9 SCL clock pulses to transfer each 8 bit byte
of data this is shown in Fig-3. If the receiving device sends back
a low ACK bit, then it has received the data and is ready to
accept another byte. If it sends back a high then it is indicating it
cannot accept any further data and the master should terminate
the transfer by sending a STOP sequence. In Fig-2(b) which
shows the STOP sequence, where the SDA line is driven low
while SCL line is high. This signals the end of the transaction
with the slave device.
2.2 Serial Data Communication
The I2
C bus has two modes of operation: master transmitter and
master receiver. The I2
C master bus initiates data transfer and
can drive both SDA and SCL lines.[2] Slave device is addressed
by the master. It can issue only data on the SDA line.
In master transmission mode, after the initiation of the START
sequence, the master sends out a slave address. The address byte
contains the 7 bit slave address, which is followed by the
direction bit (R/ w). After receiving and decoding the address
byte the device outputs
Acknowledge on the SDA line. After the slave device
acknowledges the slave address + write bit, the master transmits
a register address to the slave this will set the register pointer on
the slave. The master will then begin transmitting each byte of
data with the slave acknowledging each byte received. The
master will generate a stop condition to terminate the data write.
In master receiver mode, the first byte is received and handled as
in the master transmission mode. However, in this mode, the
direction bit will indicate that the transfer direction is reversed.
Serial data is transmitted on SDA by the slave while the serial
clock is input on SCL. START and STOP conditions are
recognized as the beginning and end of a serial transfer (Fig-5).
The address byte is the first byte received after the start
condition is generated by the master. The address byte contains
the 7-bit slave address, which is followed by the direction bit (R/
w). After receiving and decoding the address byte the device
inputs acknowledge on the SDA line. The slave then begins to
transmit data starting with the register address pointed to by the
Fig-3 Acknowledgement on the I2
C Bus register
Pointer. If the register pointer is not written before the initiation
of a read mode, the first address that is read is the last one stored
in the register pointer. The slave must receive a “not
acknowledged” to end a read.
Fig -4 Master Transmission Mode
Fig- 5 Master Receiver Mode
The master transmission mode and master receiver mode is
shown in above figure.
3. SOFTWARE IMPLEMENTATION
I2
C bus is a medium for communication where master controller
is used to send or receive data to and from slave and it is
developed by Philips.
I2
C master controller is designed using Verilog HDL [3] based
on Finite State Machine (FSM) [8]. FSM is a sequential circuit
that uses a finite number of states to keep track of its history of
operations, and based on history of operation and current input,
determines the next state. There are several states in obtaining the
result.

3. IJRET: International Journal of Research in Engineering and Technology eISSN: 2319-1163 | pISSN: 2321-7308
__________________________________________________________________________________________
Volume: 03 Special Issue: 03 | May-2014 | NCRIET-2014, Available @ http://www.ijret.org 412
Algorithm
State 1: An idle condition: I2
C bus doesn’t perform any
operation. (SCL and SDA remains high).
State 2: Start condition: master initiates data transmission by
providing START (SCL is high and SDA is from high to low).
State 3: Slave address - write: master sends the slave address-
write (11010000) to the slave.
State 4: If the slave address matches with the slave, it sends an
acknowledgement bit in response to the master.
State 5: 8 Bit Register Address[7] will be transmitted to the
slave. Again acknowledgement is sent to the master by the slave.
State 6: Data to be transmitted is sent to the slave by the master.
After receiving the data, slave acknowledges the master.
State 7: Stop condition: Slave sends a stop bit to the master to
terminate the communication (SCL is high and SDA is from
Low to high).
State 8: Master transmits slave address for read operation to the
slave.
State 9: Master receives the data from the slave and
acknowledges the slave.
State 10: Master sends a STOP bit to terminate the connection
(SCL is high and SDA is from Low to high).
For performing read operation, write operation is performed first
and then read operation is done. Slave address for read is
11010001. (State 7 will not be performed for read operation)
Fig 6: Flow chart of I2
C master bus controller.
Fig-8 shows the flowchart for I2
C master bus communication
with slave device. Fig-9 shows the Modelsim simulation result
for write operation, the given data input is written in to slave
register address in each state of FSM programmed in Verilog
HDL. Fig-10 shows the Modelsim simulation result for read
operation, to read the written data from the slave the write
operation takes place first followed by the repeated start
condition and sending the slave address read (11010001) in each
state of FSM.
The simulated Verilog coding is synthesized on Spartan 3AN
through Xilinx ISE Design Suite14.2 [4]. The design is analysed
using ChipScope Analyzer in Spartan 3AN platform.
Fig-7.Modelsim Simulation Result for Write operation
Fig-8 Modelsim Simulation Result for Read operation
After completing the coding in Verilog HDL, it is downloaded to
the Spartan 3AN kit using Xilinx software. And corresponding
input is given according to the I2
C protocol.
4. CONCLUSIONS
I2
C bus controller is successfully designed in verilog and
simulated in ModelSIM. Simulation results verify that the
communication has been established between the multi master
and the multi slave.
REFERENCES
[1]. Philips Semiconductor “I2C Bus Specification” version 2 1,
January 2000.
[2]. Raj kamal ,“Embedded system: Architectureprogramming
and Design”,Tata McGraw Hill,2008.
[3]. Stuart Sutherland, “Verilog® HDL Quick Reference Guide”,
IEEE Std 1364-2001.

4. IJRET: International Journal of Research in Engineering and Technology eISSN: 2319-1163 | pISSN: 2321-7308
__________________________________________________________________________________________
Volume: 03 Special Issue: 03 | May-2014 | NCRIET-2014, Available @ http://www.ijret.org 413
[4]. Xilinx “Spartan-3A/3AN FPGA Starter Kit Board User
Guide,”version 1.1,2008.
[5]. A.P.Godse, D.A.Godse, “Microprocessor, Microcontroller &
Applications”Technical publications, 2008.
[6] .Vincent Himpe, “Mastering the I2C bus” Elektor Verlag
publications, 2011.
[7]. M.Morris Mano, “Digital Design” EBSCO publishing.Inc.,
2002.
[8]. Frank Vahid, “Digital Design with RTL Design, Verilog and
VHDL”VP and Executive publisher, 2010.